The present invention relates to a method of tuning a microwave integrated circuit broadly, and more particularly to the trimming of predetermined film type circuit patterns thereof by a cold pressure bonding technique.
Recently, a great deal of interest has been generated by the research which scientists are doing on gallium arsenide integrated circuits, especially those of the power application variety. These small-lightweight high performance devices show great promise of being cost competitive. However, achieving this goal of low cost is predicated on the ability to trim the film-type circuit patterns included in these integrated circuits. For example, it has been indicated that if it is assumed that a circuit can be manufactured with one tuned circuit to 20% yield, then, assuming a Price-Like Statistical distribution (i.e. that which accounts for localized regions of a wafer having higher yield than other regions of the same wafer), it is found that for a two-mask process, the in-spec yield of 20 film-type impedance elements of the circuit would be less than 0.2%, which is fully unacceptable. It is well understood that analog tuning methods can increase the population of acceptable chips.
If the size of conventional microwave integrated circuits, like those implemented by microstrip technology, for example, are contrasted with recently developed gallium aresenide power integrated circuits a 50-100 to 1 miniaturization ratio is commonly realized. However, while on one hand this appears to be a benefit, on the other hand because of the small size many problems are manifested in the methods used for tuning the various circuits thereof. For example, the very small gallium arsenide integrated circuits do not respond well to the conventional laser tuning method because of the heating associated with this method which causes the gallium arsenide to lose stoichiometry and become conducting. That is, the heating of the laser beam has a tendency to drive off the arsenic from the gallium arsenide substrate leaving the integrated circuit with a different substructure and properties. An even more severe problem is that when heating with a laser beam, the metal conductive paths on the surface of the gallium arsenide substrate of the integrated circuit suffer metal splatterings which are deposited indiscriminately across the surface causing, at times, detrimental shorting of the circuit paths thereof.
Another well known method for tuning these gallium arsenide integrated circuits is the use of wire bonding techniques. While this method is entirely possible on the gallium arsenide integrated circuits, it is difficult to accomplish with precision and additionally requires that the substrate be heated to temperatures in excess of 200.degree. C. or so before the large wire bonds will flow together with the metal contacts.
Another area of concern is in those cases in which the integrated circuit is coupled to a microwave test fixture for in-situ testing during the tuning procedure thereof. Under these conditions, the heat requirement becomes a real problem since the microwave measurements must be interrupted between every tuning adjustment. More specifically, the microwave test fixture has to be recalibrated after each tuning adjustment, making precise subtle tuning adjustments very difficult. These and other heating type problems associated with the tuning of the integrated circuits are proposedly alleviated by the inventive method disclosed herein in that the process for trimming the film type circuit patterns, like inductances and capacitances, for example, may be performed without the use of any heat treatment.